Numerous processes are within the purview of those skilled in the art for forming toners. Emulsion aggregation (EA) is one such method. EA toners are generally formed by aggregating a colorant with a latex polymer formed by emulsion polymerization. For example, U.S. Pat. No. 5,853,943, the disclosure of which is hereby incorporated by reference in its entirety, is directed to a semi-continuous emulsion polymerization process for preparing a latex emulsion by first forming a seed polymer. Other methods of emulsion/aggregation/coalescing for preparing toners are illustrated in U.S. Pat. Nos. 3,644,263; 3,879,327; 4,243,566; 5,403,693; 5,418,108; 5,364,729; 5,346,797; 5,527,658; 5,585,215; 5,650,255; 5,650,256; 5,501,935; 7,683,142; 7,977,024; 8,124,309; 8,163,459; and 8,168,699, the disclosures of which are hereby incorporated by reference in their entirety.
Polyester toners with low melt properties can be prepared using amorphous and crystalline polyester resins. These polyesters must be formulated into emulsions prepared by solvent containing batch processes before they can be incorporated into the toners. The solvent-containing batch processes include, for example, solvent flash emulsification and/or solvent-based phase inversion emulsification (PIE).
U.S. patent application Ser. No. 13/686,374, discloses an apparatus and a method for preparing a latex or emulsion using a batch process, the method comprising contacting a resin with an organic solvent and an optional neutralizing agent to form a resin mixture; and introducing steam to the resin mixture to form the latex or emulsion.
Batch processes can be difficult to scale up because their process inputs (e.g., resin acid values, solvent evaporation rates, and neutralization agent evaporation rates) could vary and, thus, could cause a wide range in process noises, making both accuracy and precision between batches (i.e. batch-to-batch variations) difficult. As a result, a large amount of time and materials could be wasted by taking a trial and error approach, even at laboratory scale, to determine a critical point for preparing latexes with various desired particle sizes.
Moreover, if quality standards are not met for a particular batch, an entire batch has to be rejected. Because the batch processes sometimes cannot be immediately interrupted, preventing further waste of raw materials (which could be sent back for reprocessing) is often not accomplished. Although batch processes are often used, a batch process can be inherently wasteful and can often complicate future project planning for a green process with reduced chemical disposals and mechanical maintenance fees.
Additionally, conventional PIE processes typically use mechanical agitation, which may not be able to sufficiently and reliably control the mixing efficiency throughout a whole reaction vessel due to the non-Newtonian behavior of liquid-phase materials during the emulsification process. A high mixing field only localizes at the impeller tip, and the mixing strength decreases away from the impeller, especially along the vessel wall region. Also, dead spots or shallow spots with inefficient mixing can be distributed along the edge of the shaft. Further, establishing a more efficient and more complex impeller design might increase cost. Thus, batch-to-batch consistency can be difficult to achieve at this stage.
Accordingly, continuous processes have been explored throughout the industry. For example, U.S. Patent Application Publication No. 2011/0015320, the disclosure of which is hereby incorporated by reference in its entirety, discloses a process and system for use in forming toner particles using at least one micromixer for mixing a resin mixture and an aqueous phase to continuously produce an emulsion having a high solids content.
Another example is U.S. Patent Application Publication No. 2001/0313079, the disclosure of which is hereby incorporated by reference in its entirety, which discloses a solvent-assisted extrusion process for forming high yield, low coarse content, polyester latexes that may be utilized in forming a toner.
It would be advantageous to provide a method for preparing a latex or dispersion suitable for use in a toner product that is more efficient, takes less time and results in a more consistent toner product than conventional methods for making toner.